Black tie is a semi-formal Western dress code for evening events, originating in British and North American conventions for attire in the 19th century. In British English, the dress code is often referred to synecdochically by its principal element for men, the dinner suit or dinner jacket. In American English, the equivalent term tuxedo is common. The dinner suit is a black, midnight blue or white two- or three-piece suit, distinguished by satin or grosgrain jacket lapels and similar stripes along the outseam of the trousers. It is worn with a white dress shirt with standing or turndown collar and link cuffs, a black bow tie, typically an evening waistcoat or a cummerbund, and black patent leather dress shoes or court pumps. Accessories may include a semi-formal homburg, bowler, or boater hat. For women, an evening gown or other fashionable evening attire may be worn.

Western dress codes are a set of dress codes detailing what clothes are worn for what occasion. Conversely, since most cultures have intuitively applied some level equivalent to the more formal Western dress code traditions, these dress codes are simply a versatile framework, open to amalgamation of international and local customs. This versatility has made this scale of formality a practical international formality scale.